1. Field of the Invention
This invention relates to a simulator which is used in combination with a detachable control unit for a nuclear reactor refueling machine to simulate inputs to the control unit without it actually being installed on the machine, and is useful for operator training and testing.
2. Prior Art
A reactor refueling machine is a device used to remove and replace, or rearrange, fuel assemblies and other components in the core of a shutdown nuclear reactor. Typically such a machine comprises a bridge which moves reciprocally on horizontal tracks straddling the water filled pit in which the reactor vessel is housed. A trolley is mounted on the bridge for reciprocal horizontal movement along the bridge so that by appropriate movement of the bridge and trolley, a mast assembly mounted vertically on the trolley can be positioned over any desired location in the pit. The mast assembly includes an inner mast telescopically mounted inside a fixed mast. A hoist mounted on the trolley raises and lowers the inner mast which carries on its lower end grippers for engaging and lifting fuel assemblies. When a fuel assembly has been lifted clear of the reactor vessel by the hoist, the bridge and trolley are repositioned to locate the fuel assembly over a new location in the core, or to move the fuel assembly to a storage area in the pit or to a transfer system which removes the fuel assembly from the pit. New fuel assemblies supplied through the transfer system are inserted in the core by reverse operation of the refueling machine.
Some of the newer refueling machines also have mechanisms for transferring separately from the fuel assemblies other reactor components, such as fuel rod clusters and control rod thimble plugs. An example of such a machine is described in U.S. Pat. No. 4,511,531. In this machine, a rod telescoped inside the inner mast carries grippers adapted to engage these other reactor components. The hoist is connected to this rod, which in turn is selectively coupled to the inner mast by lugs on the rod which engage a pivotable stop plate on the inner mast. With the stop plate raised, the inner mast is raised and lowered with the rod for servicing fuel assemblies. With the stop plate lowered, the rod moves independently of the inner mast for servicing the other reactor components.
The bridge, trolley and hoist of a refueling machine are positioned independently by separate motors. These motors are controlled by an operator from a control console mounted on the trolley. Signal generators generate feedback signals indicative of movement of each of these components in response to operation of the respective motors. The control console uses these signals in a control loop to accurately position these components and to generate indications to the operator of their respective locations. In the refueling machine disclosed in the above cross-referenced application, the feedback signal generators produce pulses representative of incremental movement of the respective components. The control console includes a programmed digital computer which counts the pulses to track movement and generate a visual display of component position on a cathode ray tube.
The earlier control consoles for reactor refueling machines utilized relay logic which is relatively immune to the harsh conditions inside containment, and therefore these units were left in place on the trolley during operation of the reactor. The digital computer and its associated interfaces are less tolerant of the high temperature, humidity and radiation levels found within containment during reactor operation. Since the refueling machine has no function during reactor operation, it has become the practice to remove the control console from containment during plant operation and to place it in storage until the next refueling cycle.